Delays seen unlikely along US-Canada border

Customs and Border Protection officers will issue warnings to most people who lack the correct documents and use discretion in detaining people for questioning, said Jayson Ahern, acting customs commissioner.

The United States "will have a flexible enforcement policy on June 1," he told reporters. Eventually, "we'll get to a point where" full compliance will be required, he said.

The new requirements are part of an initiative begun by the Bush administration and continued under President Obama to make it harder for terrorists to enter the country.

US security officials have said the US-Canada border, crossed by 400,000 people daily, is porous, potentially offering prime entry points for terrorists.

Ahern estimated that as many as 90 percent of those crossing will have the right documents on June 1.

Customs officials took a similar approach last year when they began requiring travelers to provide proof of citizenship. While business and industry officials praised that effort for minimizing delays, they said it's unwise to impose new rules during an economic crisis.

"Any delay, any bottleneck, any legitimate traveler not able to go across to service a piece of equipment or for a legitimate business purpose is a problem," said Shaun Donnelly, senior director for international business policy at the National Association of Manufacturers, a Washington-based lobbying group.

Some of those fears may be unfounded because companies that frequently do business across the border will be prepared, said Christopher Sand, a senior fellow at the Hudson Institute, a policy research organization in Washington.